1. Field of the Invention
The present invention relates to a fuel injection apparatus for injecting a fuel, for instance, to an internal combustion engine, and more specifically to a fuel injection apparatus for controlling a fuel injection rate by a fuel pressure.
2. Description of Related Art
Conventionally, as a fuel injection apparatus for injecting a fuel, for instance, to an engine, there has been one equipped with a fuel injector capable of controlling a fuel injection rate by making use of the fuel pressure. This fuel injector has two fuel chambers provided at both sides of a plunger provided inside the fuel injector, and timing for injecting the fuel is adjusted by making use of the fuel pressure in one of the fuel chambers, and the fuel injection rate is adjusted by making use of the fuel pressure in another fuel chamber. Fuel feed to these two fuel chambers is performed from a fuel tank by operating a common fuel pump, and a fuel conduit is branched in the downstream from the fuel pump to a timing rail connected to the fuel chamber for controlling the timing for fuel injection and a fuel rail connected to the chamber for controlling the fuel injection rate. Each of the timing rail and the fuel rail has a pressure control valve, and the fuel is fed to each of the fuel chambers by adjusting a pressure of the fuel from the fuel pump with this pressure control valve.
In the fuel injector as described above, a higher fuel pressure as compared to that in the fuel rail is required in the timing rail, so that the common fuel pump generally feed a fuel according to the higher pressure required in the timing rail. Therefore, in the fuel rail, it is necessary to substantially reduce the fuel pressure in the fuel rail with the pressure control valve, and a difference between pressures before and behind the pressure control valve becomes large. When this pressure difference becomes larger, air bubbles are generated in the pressure control valve, and sometimes the pressure control disadvantageously vibrates. When this phenomenon occurs, fluctuation occurs in the fuel pressure to cause variation in the fuel injection rate, which in turn cause fluctuation in a revolution speed of the engine. Further vibration in the fuel pressure may occur in association with the vibration of the fuel pump.
A main object of the present invention is to provide a fuel injection apparatus in which vibration of a fuel pressure can be reduced to feed a fuel at a stable fuel injection rate. To achieve this purpose, the fuel injection apparatus according to the present invention has a unit for absorbing the pressure vibration provided therein. The configuration is described in detail below.
The fuel injection apparatus according to the present invention comprises a fuel injector having a fuel chamber with the fuel injection rate therefrom controlled by the fuel pressure having a fuel chamber for temporally storing therein a fuel to be injected; a fuel tank for storing therein a fuel; a fuel pump for pumping the fuel from the fuel tank and sending the fuel to the fuel chamber; a discharge line provided between the fuel pump and the fuel chamber; a pressure control valve provided in the discharge line for controlling a pressure of the fuel to be sent to the fuel chamber; and a pressure damping chamber provided between the pressure control valve and the fuel chamber.
In this configuration, as the pressure damping chamber is provided between the pressure control valve and the fuel chamber, vibration of the fuel pressure generated in the pressure control valve is absorbed and reduced in the pressure damping chamber to insure the stable fuel injection rate. For instance, when this fuel injection apparatus is used in an engine driving a generator, fluctuation in a revolution speed of the engine decreases in association with stabilization of the fuel injection rate, so that also a frequency of the generated electricity stabilizes. Because of this feature, when the generator is used concurrently as a power source for business use, it is easy to synchronize the frequency to that of commercial power.
In the fuel injection apparatus according to the present invention, the pressure damping chamber is preferably provided near the pressure control valve.
In this configuration, as the pressure damping chamber is provided near the pressure control valve in which vibration of the fuel pressure is generated, the vibration is effectively reduced, which enables a more stable fuel injection rate.
In the fuel injection apparatus according to the present invention, the pressure damping chamber is preferably a branch pipe branched from the discharge line with the top edge closed.
In this configuration, as the pressure damping chamber comprises a branch pipe, if the branch pipe is manufactured, for instance, with a tubular member, the branch pipe can easily be manufactured and the price is cheap. Further the branch pipe has a slender form, so that the branch pipe can easily be installed even in a narrow engine room, which insure a higher degree of freedom in designing. Because of this feature, it is also easy to additionally install the branch pipe in an engine already installed.
In the fuel injection apparatus according to the present invention, the branch pipe preferably extends in a direction along a flow of the fuel just before the branch pipe.
In this configuration, as the branch pipe extends along the direction of the fuel flow, vibration of the fuel pressure is easily delivered to the branch pipe, so that the vibration is more effectively reduced.
In the fuel injection apparatus according to the present invention, capacity of the pressure damping chamber is preferably not less than one fifth of that of the discharge line between the pressure control valve and the fuel injection chamber.
In this configuration, as a capacity of the pressure damping chamber is set to a value just suited to the purpose, vibration in the fuel pressure is fully communicated to and absorbed into inside of the branch pipe. It is to be noted that, if the capacity of the pressure damping chamber is less than one fifth of that of the discharge line between the pressure control valve and the fuel chamber, the vibration of the fuel pressure generated in the pressure control valve is not fully communicated to the branch pipe, and the vibration can not effectively be reduced.